You Used to Be a Muggle Too. Can You Do It?

It was already dark when we left St. Mungo's's.

Instead of heading straight back to the castle, Gavin turned into a less-traveled path on the side of the courtyard, stopped in the shadow of an old yew tree, leaned against its rough bark, and pulled the Marauder's Map from inside his robe.

He ran his finger along the crease, unfolded the book, and recited the command.

First, let's look at the Headmaster's Office; it's empty.

Dumbledore's name wasn't on it—uncommon, but not unexpected. He would occasionally go out, sometimes to Wizengamot, sometimes for other reasons, and he never informed anyone.

Gavin pressed his thumb down along the old crease at the fold, his gaze sweeping over the Third Floor, then over the fourth floor, and then stopped.

Quirrell.

The name was posted on the Third Floor Corridor, not far from the Trophy Room. Turn one more corner ahead, and you'll find the no-entry corridor; the name was being moved there.

Gavin stared at the small black dot for a moment, and after confirming that it had entered the room, Gavin raised an eyebrow, not expecting this moment to arrive so soon.

He refolded the map, aligned the creases, tucked it inside his robe, then stepped out from under the trees and set off back to the castle.

At this moment, the Great Hall was as lively as a pot of simmering soup.

The Hufflepuff Long Table area was particularly exaggerated.

Hufflepuff's perfect record in the Quidditch Cup is a fact that some people still find hard to believe, so they express their belief by making a huge fuss: Pumpkin Juice is poured overboard, glasses clink together, some people tie yellow and black scarves on their heads, and others stand on benches and tap their plates with forks to keep time.

Hufflepuff's suitor Tamsin Appleby, was being dragged along by several upperclassmen to recount the game against Gryffindor. He'd already told it about fifteen times, but he clearly wasn't tired of it yet.

Gryffindor isn't too bad either.

Slytherin lost, which lessened most of the frustration. The twins were making something out of Mashed Potatoes at the end of the Long Table, while Percy, eight seats away, was trying to kill with his eyes.

Harry, Ron, and Hermione sat close together at the Gryffindor table, Hermione lips moving rapidly. Ron frowned, his fork poking at a piece of Yorkshire pudding on his plate for a long time without putting it in his mouth.

Gavin walked around behind them, leaned down, and lowered his voice to a level much quieter than the noise in the Great Hall.

"Dumbledore is not at school today."

All three looked up at the same time. Harry's fork froze in mid-air. Ron had something in his mouth, his cheeks bulging, and his eyes wide open. Hermione had already pushed her chair back half an inch.

Gavin glanced at Harry, then shifted his gaze to Hermione's face. "I saw Quirrell go into that room on the fourth floor."

Ron nearly choked on the Pudding in his mouth, and he coughed lightly, "Now?"

"Now."

"Wait a minute, Quirrell?" Harry stared at Gavin in disbelief.

Gavin nodded and said, "It seems you've suspected the wrong person."

Hermione frowned. "Is it possible that Snape forced him to go?"

Gavin shook his head. "I don't know yet, but he's already inside."

"How did you know?" Harry asked hesitantly, still reeling from the shock of it being Quirrell instead of Snape.

"I have my methods, and I can guarantee they will be accurate."

Hermione stood up, the chair leg scraping against the stone floor with a short, sharp sound. Several Gryffindor next door glanced over, then turned back to continue discussing the details of Slytherin's loss.

"What do we do now?" Hermione asked, looking at the group.

Harry thought for a moment, then said, "I'll go find Professor McGonagall."

After saying that, he jogged towards the High Table and stopped Professor McGonagall, who was about to leave.

Harry kept talking, while Professor McGonagall just shook her head. A little while later, Harry Gavin all.

Harry described what had happened in frustration, concluding, "She doesn't believe me. She just told us to wait until Professor Dumbledore returns tomorrow."

"Tomorrow?" Ron jumped up, then lowered his voice after noticing the surprised looks from the other Gryffindor beside him. "It will be too late by tomorrow."

Harry nodded. "We have to stop him."

"Well done, Ron." Gavin silently gave Ron a thumbs-up in his mind.

"Shall we leave now?" Hermione asked.

"I need to go back and get some things." Gavin thought for a moment; he needed to go back and get some equipment and props. "I'll come find you guys later."

"Where shall we meet?" Harry asked in a low voice.

"Let's go to the Third Floor Corridor," Gavin said. "Don't go up together. It'll be too conspicuous."

Hermione nodded, completely switched into that uncompromising execution mode, her chin slightly tucked in, shoulders tense, her fingers unconsciously hooking the edge of her robe pocket at her side.

Ron swallowed what was in his mouth, picked up the cup, and took a big gulp of Pumpkin Juice, as if to bolster his courage.

"We're coming right away," Harry said.

Gavin straightened up. Just as he was about to leave, Ron called him back.

"Gu."

"Um?"

Ron opened his mouth, as if to say something, but in the end, he only managed to say, "You'll come, won't you?"

Gavin glanced at him.

"Of course, I'm just going back to my dorm to get something."

He turned and left after saying that.

The revelry in the Hufflepuff Common Room was more concentrated than in the Great Hall.

The space was small and crowded, so the sounds bounced back and overlapped from the circular stone walls. The low ceiling muffled every cheer to twice the decibel level.

Food was laid out everywhere, not the delicate snacks made by House-elf, but things made by the older students themselves.

Plates of crooked Butter Biscuits, unevenly spread chocolate sauce, and magically whipped cream piled up like a lopsided tower—someone poured Pumpkin Juice into a large bowl borrowed from the kitchen, tossed in half a handful of crackling sugar, and green and golden sparks kept popping on the surface of the liquid.

Gavin planned to sneak along the wall. He knew the route from the barrel entrance to his dormitory very well. Normally, he only needed to walk through half of the lounge, hug the Fireplace side to avoid the densest crowd, and then turn into the corridor on the right.

He mentally reviewed the route, lowered his shoulders, and began to move along the wall.

But he didn't make it.

"Gu is there!"

It was Ernie who shouted. Ernie was standing on the sofa, holding half a cookie in one hand and pointing at Gavin by the door with the other. His face was flushed, and he looked like he had drunk at least three glasses of Pumpkin Juice —or something mixed in with Pumpkin Juice.

The noise in the lounge stopped for a second, then it was as if someone had poured a ladle of water into a pot of hot oil.

Everyone turned their heads at the same time. Several older students jumped up from their chairs. Herbert Fawley squeezed through the crowd from the other end, bumping and jostling with his shoulders to clear a path. His expression was as if he had seen a golden mole walk into its cage.

"Don't let him get away!" someone shouted.

The crowd surged toward him, Gavin's toes had just turned toward the dormitory when two hands grabbed his shoulders from behind.

His technique was very professional—it was the result of three years of Quidditch practice, specifically designed to catch Bludger.

He was flipped over, and several hands reached out to lift him up, his feet off the ground. He felt himself flying, the distance between him and the ceiling suddenly getting closer and then suddenly getting farther away.

The moment my body was tossed into the air, my stomach sank down, then I fell back into a net woven from palms, tossed again, and fell again.

Cheers erupted with each rise and fall; some clapped, some stomped their feet, and some tapped their cups with forks in a series of off-key rhythms.

After a long time—enough for Gavin to read at least the introduction of a paper—the group reluctantly put him down on the sofa.

Herbert personally pressed his shoulder to help him sit down, his movements conveying a sense of calm that said, "You can run, but if you run, I'll catch you again."

Herbert looked at Gavin and said seriously, "This must be made clear today."

"Gu, you have to take responsibility." Someone nearby spoke with overwhelming force.

Gavin was pulling his robe collar back into place, his fingers pinching the collar edge and pulling it down a little, when he heard this, he stopped.

What am I responsible for?

"You're responsible for telling me how you trained Cedric." Herbert's hand remained firmly on his shoulder, his thumb pressing on his shoulder blade, not too hard, but with no intention of pulling away. "Now the whole academy knows."

Gavin's eyelid twitched. "Who said that?"

Everyone around turned to look at Cedric.

Cedric was leaning back on the sofa armrest, holding a barely touched glass of Pumpkin Juice, a smile that was somewhere between smug and guilty on his face. When all eyes turned to him at once, he quickly wiped the smile off, raised the glass to his lips, and used the rim to cover the lower half of his face.

"I only told you part of it." He sounded a little guilty, his voice muffled behind the glass.

Gavin looked at him for a moment and said, "You don't usually have this ability."

The people around him had already started laughing, but Justin laughed the loudest. After laughing, he took a half step back and shrank behind Ernie, only showing half of his head. He knew very well that the person who laughed the loudest in this situation was most likely to become Gavin's next target.

"Gu, don't change the subject." Herbert didn't smile; his eyes held the same look he did during Quidditch tactical meetings—focused, unwilling to let anyone leave. "You have to say it today. Everyone wants to know. Why can Cedric always spot the Golden Snitch so quickly?"

"Right."

Tell me about it.

Just a little.

"We won't steal too much from them."

The last sentence was shouted by someone hiding in the back of the crowd, and even the person who said it couldn't help but laugh.

Herbert stared intently at him, and everyone around him was also staring back at him without blinking.

Gavin glanced towards the entrance to the lounge, mentally calculating the time. Quite some time had passed, and he wondered if Harry and the others were still waiting for him. He began to regret not using the Disillusionment Charm to conserve Magic; he had assumed no one would notice him.

The people in this room clearly wouldn't let him leave easily.

"Alright." Gavin leaned back against the sofa cushions, abandoning all hopes of escaping anytime soon. "Let's get this straight, I'll only say it once. If you don't understand, that's your problem."

The surroundings quieted down considerably, and most people nodded, their faces displaying a confident expression—what was there to misunderstand?

Herbert shoved a glass of Pumpkin Juice into his hand, as attentive as if he were offering a libation to the professor.

Gavin glanced down at the glass of Pumpkin Juice, but instead of picking it up, he pushed it aside to prevent it from being knocked over.

"First, you need to understand one thing: the Golden Snitch is a magical item." He cut straight to the point, without mincing words. "And magical items are not truly living beings; they don't have their own consciousness."

Herbert immediately chimed in, "Everyone knows that. Of the Five Exceptions Gamp's Law of Elemental Transfiguration, life cannot be created."

The older students around nodded in agreement, while a few first-graders looked at each other blankly, not knowing what it was, but too embarrassed to ask.

Gavin nodded. "So, the Golden Snitch only operates according to pre-set rules—or habits. Its trajectory may appear random at any given moment, but if you extend the observation scale, its probability distribution in space is deterministic."

After those words were spoken, a brief silence fell over the lounge.

Everyone started exchanging bewildered glances, feeling as if they had just heard English, but when put together, it was all words they couldn't understand. It was like knowledge had flowed through their brains, but nothing had been retained.

Someone asked in a low voice, "What does that mean?"

Gavin turned towards the direction of the voice, his tone unchanged. "It means we can predict where the Golden Snitch will appear in the near future by observing its movement."

Herbert opened his mouth. He understood the conclusion, but hadn't followed the reasoning. His mouth was agape, his face screaming, "Is this even possible?!"

Heidi MacAvoy, the Chaser, peeked out from the front row, her brow furrowed even deeper than Herbert's. "But the Golden Snitch just flies around randomly. I've been Seeker before, and it always appears in a different spot."

"Of course they're different," Gavin said. "But have you noticed that it never flies out of bounds?"

"Of course--"

"So firstly, its activity range is restricted to a space with clear boundaries." Gavin continued, speaking slightly faster than usual, but still enunciating each word clearly. "Using the center of the court as the origin, establish a spatial rectangular coordinate system—the X-axis along the long side of the court, the Y-axis along the short side, and the Z-axis vertically upward. The Golden Snitch's position at any given time can be represented by a set of three-dimensional coordinates. Next, divide the area where it might appear within ten seconds into several probability units. This probability distribution is not uniform— the Golden Snitch's probability of staying near the boundary is lower than in the center, and its probability of turning back near the stands is higher than on the side farther from the stands. Then, you substitute the day's wind speed, wind direction, air humidity, and temperature into correction parameters, making a weighted adjustment to the probability distribution, and you can obtain the area where it is most likely to appear next."

When he finished speaking, the lounge fell completely silent. No one responded; no one knew what to say.

A sixth-grade student sitting in the front row dropped a cookie onto his lap, breaking it into three pieces, but didn't pick it up.

Justin stood behind Ernie, his mouth slightly open, his eyes conveying a "I know he's outrageous, but this is just too outrageous" look.

Herbert was the first to recover. He slowly turned his head and looked at Cedric. "Is this what you usually practice?"

Cedric smiled happily; finally, someone understood him. He nodded vigorously.

"That's right."

"How can you possibly learn that?" Herbert's voice rose.

Cedric shrugged. "Most of the time, Gu tells me the model data for the next ten minutes in advance, and I substitute it into my actual observations and make minor adjustments on the spot, which reduces the amount of calculation much."

Herbert thought it made perfect sense; this was the Cedric he knew. He nodded, then suddenly stopped. "Why ten minutes?"

"Let me explain," Gavin took over, glancing again towards the lounge door. "Ten minutes is the upper limit of this prediction model's timeliness. Beyond ten minutes, the accumulated random bias of the Golden Snitch will exceed the model's tolerance range, causing a precipitous drop in accuracy. And—" he paused, "Even Cedric can't calculate it."

"So we either end the fight in ten minutes, or we wait to be defeated?" Herbert concluded.

Cedric immediately objected. "Hey, that doesn't mean we should just wait to fail. I can catch the Golden Snitch if I try my best—"

Herbert ignored the remark. He turned back to Gavin, his lips moving as if he were regurgitating something, before finally asking the question that had been stuck between his teeth for a moment.

"What is... xyz?"

"Mathematics," Gavin said, "A Muggle discipline used to model the world."

"Merlin," someone murmured.

"Is this still Quidditch?" a small, younger boy asked uncertainly.

"This doesn't look quite right anymore," another boy muttered, feeling his faith had been tainted.

"Shut up." Herbert turned his head sharply, his voice not loud but extremely forceful, like the tail of Broomstick striking a locker room bench. "This is the key to our continued success next year."

As soon as these words were spoken, a chorus of enthusiastic agreement erupted from the surrounding crowd.

The cup was raised, and the rough Butter Biscuits were broken apart again.

It's not that no one thinks this is outrageous—it's that the absurdity itself doesn't matter anymore. The feeling of winning is too wonderful, and they're willing to do anything for the next championship, including embracing a Muggle subject called mathematics.

Ernie had been listening intently the whole time. He wasn't shocked or distracted at all; he just tilted his head slightly, pursed his lips, and tapped his knee with his fingers.

But then he suddenly remembered something, turned around, and looked at Justin behind him.

"You're Muggle-born too."

Justin immediately had a bad feeling.

Sure enough, Ernie's next question was, "Can you do this?"

Justin stared at him for a full two seconds, during which his expression changed several times before he finally said weakly, "What do you think?"

Ernie thought about it, and thought about it some more; clearly, he was seriously considering whether there was any theoretical possibility to it.

Finally, he said, "I think, theoretically, it's possible?"

"Theoretically, I could be Minister for Magic." Justin patted Ernie on the shoulder, the pressure light but the rhythm slow, each pat like hammering a nail into a tombstone. "Why don't you help me write my campaign speech first?"

The surrounding crowd burst into laughter.

Ernie's face turned red, but the person being laughed at didn't care anymore, because everyone was laughing. Cookie crumbs sprayed from the mouth of an older student, and Herbert laughed so hard he had to prop his arms up on the back of the sofa.

"Is there anything else?" Gavin's voice cut through the laughter; he was already standing up.

Herbert wiped away the tears of laughter. "Then next year—"

"We'll talk about next year's issues next year."

"Could that modeling thing be done again—?"

"Ask Cedric," Gavin said casually, gesturing towards the armrest of the sofa as if assigning a trivial task. "He's already quite adept at it."

Cedric, who had been eating a cookie, held his hand in mid-air, his smile gradually freezing. "What?"

The crowd had turned towards him.

Herbert moved his hand off Gavin's shoulder and onto Cedric's shoulder with the same force.

Cedric cast a pleading look in Gavin's direction.

Gavin gave him a "good luck" look, then turned around. He didn't run, but his pace was much faster than usual, and in the blink of an eye, he had moved from the sofa area to the entrance of the corridor leading to the dormitory.

He pushed open the door as Cedric began explaining how to calculate the wind speed correction factor.

Upon entering the dormitory, he closed the door, leaned against it, and pulled out the Marauder's Map from the inside of his robe, unfolding it.

Gavin first checked the location of the Third Floor Corridor, and sure enough, Harry and the others weren't waiting for him there. A bad feeling welled up in his heart. Then he searched the entire map but couldn't find any black dots on Quirrell's map or the trio's map.

There's only one possibility: the Dungeon where the Mirror of Erised is located isn't on the map; it might have been newly discovered.

Harry and the others had already gone inside.

"Damn it," Gavin, sounding annoyed. "We've wasted too much time."

He folded the map, tucked it into his sleeve, picked up the small bag he had prepared beforehand, and then quickly pushed open the door and walked into the corridor.